1. Field of the Invention
Embodiments of the present invention relate to a drawing apparatus configured to perform drawing on a substrate with a plurality of charged particle beams.
2. Description of the Related Art
As such a drawing apparatus, there is a known multi-column drawing apparatus having a projection unit for each charged particle beam (Japanese Patent Application Laid-Open No. 09-007538). Since each projection unit is separately provided, the drawing apparatus does not have a crossover where all of a plurality of charged particle beams are converged in a projection system. Therefore, space-charge effect (Coulomb effect) is not much affected, and thus it can be said that the drawing apparatus is advantageous in increasing the number of charged particle beams.
However, in order to increase the number of charged particle beams in the multi-column drawing apparatus, generally, it is necessary to increase a divergence angle (divergence half angle) of a charged particle beam from a charged particle source in an irradiation optical system which is in front of the plurality of projection units. If the divergence angle of the charged particle beam from the charged particle source becomes large, it is difficult to sufficiently parallelize beams irradiated onto the plurality of projection units due to aberration in an irradiation optical system, and thus irradiation angles (incident angles) become non-uniform. The non-uniformity of the irradiation angles results in non-uniformity in characteristic among the plurality of charged particle beams. Although there has been known issues related to aberration of a projection optical system and configurations for compensating for the aberration, issues related to aberration of an irradiation optical system as mentioned above were uniquely recognized by the inventor of the present invention.